1. Field of the Invention
The present invention relates to a press for hydrostatic extrusion comprising a die which is composed of two or more individual parts. The purpose of the invention is to reduce the stresses in and around the die opening and accordingly to reduce the risk of rupture and increase the life, and also to facilitate and reduce the cost of the manufacture of the die. The die is particularly intended for hot extrusion where the high temperature of the billet increases the stresses in the die. Different kinds of equipment in which the die may be used are described more fully in, for example, U.S. Pat. Nos. 3,702,555 and 3,751,958.
2. The Prior Art
In a press for hydrostatic extrusion, a die projects into a pressure chamber and rests on a die support which takes up axial forces operating outwardly on the die. Usually the die support also projects somewhat into a cylinder which forms part of the pressure chamber. The die is surrounded by the pressure medium which acts on the billet to be extruded. The pressure medium brings about forces acting radially inwardly on the outer surface of the die. The billet to be extruded brings about outwardly acting radial forces in the inlet portion of the die. Up to the die opening these radial forces balance each other, but outside the smallest calibrating cross-section of the die opening there is a clearance between a pressed product and the die, so the forces produced by the pressure medium give rise to very great stresses at the inner surface of the die. A stress factor greater than two is obtained for thick-walled tubes in case of an outer load, that is, the stresses at the inner surface are more than twice as great as at the outer surface. The outer load itself is great, usually from 10 to 15 kbar. A die manufactured in one piece has also a shape which is less suitable from the point of view of hardening, and must of course have the same high-tensile material in the inlet portion as at the die opening, in spite of the fact that the material in the inlet portion is not subjected to the same high stresses. This results in a bad utilization of the material in the inlet portion of the die.